Magnetic recorder with pressure shoe for record members



M. CAMRAS July 15, 1952 MAGNETIC RECORDER WITH PRESSURE SHOE FOR RECORDMEMBERS FiledDec. 8, 1947 Patented July 15, 1952 r "or- MAGNETICREcoRoER wrrn PRESSURE snos FOR REooRD MEMBERS Marvin Gamras, Chicago,Ill; assignor to' Armour Research Foundation of Illinois 'InstituteofTechnology,- Chicago, Ill., a corporation of Illinois I ApplicationDecember 8, 1947, Serial No; 790,418

This invention relates .to. a

member. 7 I

In'one method of magnetic recording a lengthy magnetizab'le. recordmedium is drawn across an electromagnetic transducer head assembly atsubstantiallyv uniform linear velocity. The head assembly includes amagnetic core member having anon-magnetic cap overwhichthe mediumpasses, vand which isprovided withsuitable current conducting exciting.elementsto produce a magnetic field across the gap. I 1

Duringthe recording operation current is caused to flow in excitingelements'in accordance with time variations .of an intelligence to pro"duce a time varying magnetic field in the core in accordance with thevalue there of The lengthy magnetizable' medium is subjected to theinfiuence of this field asiit is drawn ,therethrough and magnetizationis. imparted to incremental lengthsof the medium inaccordance with thetime variations of the intelligence, thus causing variations in the.magnetization of the medium along its length in accordance with the timevariations of the intelligence, I I I During reproduction, the lengthymagnetizable medium is drawn across thesame or a similar head-assemblyto set up a flux in the core portion thereof in accordance with the.magnetization of the'mediumalong successive incremental lengths thereofas it passes across the gap of the magnetic core member. The resultanttime varying fiux induces voltage in the coil with which the fiux is Ilinked in accordance with the time rate of change thereof. I Thisvoltage may beamplified and suitably reproducedby a loudspeaker or.similar deviceto produce the intelligence recOrd6d- F I I I Thismagneticrecording and reproducing inherentlyinvolves the conversion ofan intelligence 'to a time varyingmagnetic field during-the recordingoperation andtheconversion of a time varying magnetic flux to anintelligence in the reproducing operation. It will therefore beapparent'to those skilled in the art that it is-extremely important thatthe lengthy; medium or magnetic record .member shall always bepositionedatexactly the same place with respect to the .'electromagnetictransducer head each time that itheirecord memberis'passed over thehead.

- It has-,beenfoundlto be particularly important to use some means-forclosely confining the record member to the-head whenthe. record memberis in the form of a paper tape having -magnetic recorder and moreparticularly to' a magnetic recorder having a pressure shoe for themagnetic record I I closely hug the electromagnetic transducer head e 2Claims. (01. Ive-400.2)

ama'g'netic track thereon or in'the form of a plastic film having'amagnetic track thereon. I

This invention is an improvement in the invention disclosed in my'priorUnited StatesLetters Patent No. 2,351,007 for fMagnetic Recording Head,granted June 13, 1944. I

One of the principal features and objects of the present invention istoprovide'a novel ..pressure I 'shoe structure which will conform toirregu- ,laritie s in the head or in the. record member itself so thatthe record member, such, for example, as a paper tape record member,will be caused to as it passes thereacross.

Afurther object of the present invention is to provide a novel methodand means for constantly maintaining a lengthy magnetic record. memberin continual close abutting contact with the pole of an electromagnetictransducer head irrespective of irregularities in the surface of thepole or in the record member itself. I

Another and further object, of the present inventionis to provide apressure shoe for magnetic recorders of novel construction.

Other objects and features which I believe to be characteristic of myinvention are set forth with particularity in the appended claims. My

invention itself, however, both as to its organization manner ofconstruction and method of operation, together with further objects andadvantages thereof may best be understood by reference to the followingdescription taken in I co'nnectionwith the accompanying drawing, in

which Figure 1 is a plan view of a magnetic recorder embodying the novelteachings and principles of the present invention; 7

Figure 2 is an isometric view" of an electromagnetic transducer head anderase head assembly as used on"the' magnetic recorder illustrated inFigure 1;

Figure 3- is a fragmentary elevational view partly in section of one ofthe pressure shoes ducedscale) illustrating a modified formof'pres-.sure shoe; and

Figure -6 is an elevational vicwof shoeshown'in Figure 5. As the termmagnetic recorderhis used herein,

thepressure or to a head for converting a time varying mag netic fieldto a time varying electric current, or to an erasehead in which analternating current is convertedinto an alternating magnetic field whichdemagnetizes the magnetic record member.

The novel pressure shoes of thep'resent invention may, of course, beemployed on a wide variety of magnetic recorders without departing fromthe spirit and scope of the present invention.

They have been shown in Figure 1 of the drawings as being mounted on amagnetic recorder of the dual channel one-way drive type. This recorder,generally designated as I0, includes a housing II which houses the drivemechanism and amplifying equipment (not shown). The housing II isclosedoif at the top by top panel I2 on which an electromagnetictransducer head assembly I3, the supply reel I4 and take-up reel I5 aremounted. The reels I4 and I5 are mounted on spindles I6 and II,respectively. Also mounted on the panel I2 is a capstan drive roller I8which is arranged to be driven at a uniform angular velocity from amotor drive shaft I9 through drive rollers 20 and 2|, the latter beingmounted and secured to the capstan shaft 22.

Thetake-up reel I5 is driven through a belt drive 23 from the motordrive'shaft I9. Though this drive mechanism a magnetic record member 24such, for example, as a paper tape having a coating of magnetizablematerial thereon is transferred from this sup-ply reel I4 to the takeupreel I5. The magnetic record member 24, in travelling from the supplyreel I4 to the take-up reel I 5, crosses the electromagnetic transducerhead assembly I3 and then over the capstan .drive roll I8. The driveconnection between the motor drive shaft I9 and the take-up reel I 5 isarranged 4 magnetic gap 4I between the ends of the latter. Signal coils42 and 43 are mounted on the core 38 in a similar manner to the coils 36and 31 of the erase head 26. As is the usual practice, the

non-magnetic gap M in the record play back head 21 is substantiallysmaller than the erase gap 35 in the erase head 26.

As shown, the pole portions 33 and 34 of the erase head 26- and the poleportions 39 and 40 of the record play-back head 21 cover slightly lessthan one-half of the width of the tape record member 24. The tape recordmember is thus arranged to have'two records thereon lying side by side,one extending in one direction and the other extending in the oppositedirection. Thus after the record member has been transferred from thesupply reel I4 to the take up reel I5,

the two reels may be interchanged and turned to slip as is necessary inconstant drive types of I magnetic recorders since the-take-up reel mustbe driven at a speed which tends to try to take up the magnetic recordmember faster than the capstan causes it to travel.

V The supply reel I4preferably is provided with a friction brake disk 25which maintains the magnetic record member 24 taut over the headassembly I3. I i V 4 V The head assembly I3 may be understood best froman inspection of Figure 2 of the drawing.

This electromagnetic transducer head assembly I3 includes an'erase head26 and a record playback head 21 which are mounted in -a plastic housing28 having a back Wall portion 29 which extends somewhat beyond thecurved surface 30 of the housing ,28 to provide a flange portion 3|against which the edge of the record member 24 is seated as it passesover'the electromagnetic transducer head assembly I3. The erase head 26includes a core portion 32 having a pair of con fronting polar portions33 and 34. The pole-portions 33 and 34 are slightly spaced to form anonmagnetic gap 35.];A pair of coils 36 and.31are mounted on the core32.and are electrically connected and wound to be in aiding relation toeach other in setting up a magnetic flux in the core 32. 'The recordplay-back'head 21 issimilarly constructed and includes a core 38 havingconfronting pole portions 39 and 40 with a'nonsurface of the tape.

upside down, thus placing the other half of the record member inoperative engagement withv the poles 33 and '34and the poles 39 and 40.In

. In the embodiment of the presentfinvention illustrated in Figure 1,two pressure shoes 42 and 43 are provided for holding the magnetictaperecord member 24 against the heads 26 and 21 of the electromagnetictransducer head assembly I3, These heads 42 and 43 are mountedon leafsprings 44 and'45 which, in turn, are securedin mounting posts 46 and41, respectively. The two pressure shoes "are similar in constructionso, for purposes of simplicity, only one of the shoes, namely 42, isillustrated in detail in Figures 3 and 4 ofthe drawing. As shown inFigures 3 and 4, the pressure shoe 42 includes a felt pad 48 secured toa block 49 carried on the leaf spring 44. The characteristic springinessof thefibers of a piece of wool felt is here utilized to cause therecord member '24 to, follow the possibleirregularities 50 in thesurface of the poles 33 and 34 of the head 26. This will also cause therecord member 24 to remain in close contact with the poles, even wherethere is'an irregularity in the In effect, the felt pad 48 which isspring pressed against the tape 24 by the leaf spring 44 presents a.multitude of individual pressure points over a'substantial area,

each of which tends to press the portion of the tape lying immediatelythereunder into close contact with the head. 1

In order to make it easy to slip the tape 24between the pressure shoe 42and the head, an ear 5I isprovided .at theend of the leaf spring 44which may be conveniently grasped so as to retract the pressure shoe 42to its dotted lineposition as shown in Figure 1, of the drawing. .Asimilar car 52 is also placed on the leaf spring 45.

The, post 46 may be conveniently secured to the panel I 2 by'bolts 53.The post 41 may besimilar- 1y secured to the panel I2. 1

In Figures -5 and 6,. a modified form .of the present invention is shownwherein the pressure shoes include a block 54 which is secured tothe endof the leaf spring 44. The block 54'is' provided with a plurality ofwells or recesses 55 in provided for limiting the outward movement ofthe fingers 56 so that they will not fiy out of the block 54 when thepressure shoe is flexed back away from the head against which the shoepresses the magnetic tape 24.

The fingers present a large number of relatively small pressure pointsconstantly urging the magnetic record member 24- against the poles ofthe head structure. These small pressure points define a face inengagement with the magnetic record member 24. These individually actingpressure points thus cause all of the tape to be retained in closecontact with the'poles of the head structure as the record member pas esthereover. It has been found in practice that this is greatly superiorto a single pressure shoe of rigid material which is resiliently urgedagainst the record memben i In such a construction as illustrated inFigures 5 and 6 of the drawing, it is preferable that one transverse rowof pressure fingers be located directly over the gap 35 of the head 26.A similar shoe is, of course, provided over the record playback head. Itis further desirable that the ends of the fingers 56 be rounded so asnot to damage the tape record member 24 as it passes thereunder.

It will be apparent to those skilled in the art that the upstandingposts 46 and- 41 may be constructed for manual rotation when it isdesired to retract the pressure shoes out of engagement with the medium.Moreover, rotation of these posts permits adjustment of the springpressure on the shoes and hence the total force exerted on the pressurepads.

While I have shown certain particular embodiments of my invention, itwill, of course, be understood that I do not wish to be limited theretosince many modifications may be made; and I therefore contemplate by theappended claims to cover all such modifications as fall within the truespirit and scope of my invention.

I claim as my invention; I 1. An electromagnetictransducer head assemblycomprising a core having a pair of confronting 4 pole pieces andanon-magnetic gap between their extremities, said confronting polepieces each having a surface portion over which a magnetic record memberis arranged to successively pass, a shoe mounted opposite said polepieces and having a record member-engaging portion "positioned to engagea record member over both member against said core over both of saidpole 7 pieces and said gap.

2. An electromagnetic transducer head assembly comprising a corehaving-a pair of confronting pole pieces and a non-magnetic gap betweentheir extremities, said confronting pole pieces each having a surfaceportion'over which a magnetic record member is arranged to successivelypass, a shoe mounted opposite said pole pieces and having arecordmember-engaging portion positioned to engage a record member overboth of said pole pieces and over said gap, said shoe inculding afelt-like pad forming a record member contact area, and means for urgingsaid shoe toward said pole pieces and said non-magnetic gap, wherebysaid felt-like pad positively presses a record member against said coreover both of said pole pieces and said gap.

' MARVIN CAMRAS.

REFERENCES CITED The following references are of record in the

